Town officials and residents have until Aug. 30 to submit comments to MassDevelopment regarding Forbes Hill, a proposed 300-unit housing development off Upland Road. Davis Marcus Partners is seeking a project eligibility letter from MassDevelopment, the state’s finance and development agency, in order to build the project under the state’s Chapter 40B affordable-housing statute. The plan for Forbes Hills calls for 20 percent of the units to be designated affordable for households earning 50 percent of the area median income. The proposal calls for 161 one-bedroom, 123 two-bedroom, and 16 three-bedroom units. Kelsey Abbruzzese, spokeswoman for MassDevelopment, said the agency would probably make a decision on the eligibility letter about 60 days after the public comment period. If Marcus Davis Partners gets the letter, it could then submit an application to the town’s Zoning Board of Appeals.